1. Field of the Invention
The present invention relates to petroleum and gas recovery devices and in particular to perforating guns used to perforate well pipes in oil or natural gas wells.
2. Related Art
Generally speaking, oil or natural gas may be extracted from the earth by drilling a well into a suitable earth formation. A metal well pipe or casing is inserted vertically into the well to a depth corresponding to the location of the oil or gas, and concrete is inserted into the annular space between the exterior of the well pipe and the well. When it is desired to cause gas or oil to flow into the pipe for extraction, a perforating gun is inserted into the well pipe to the depth from which it is desired to recover oil or gas. The perforating gun conventionally comprises a closed metal cylinder containing a fireset (circuitry and controls to initiate the explosives contained in the perforating gun) and a plurality of penetrating shaped charges that are fired to horizontally perforate the well pipe, allowing oil or gas to flow into the pipe and to the surface for recovery. The closed metal cylinder of the perforating gun serves to protect the explosive shaped charges and the fireset from heat, pressure and damage from water or other contaminants in the well pipe, prior to firing.
In an alternative prior art configuration, a plurality of encased shaped charges are suspended by metal chains within the well pipe at various appropriate positions. Conventionally, the shaped charges are fired using a firing signal transmission line that extends to the surface of the well site. In either case, the explosive shaped charges horizontally penetrate the well pipe and the hardened concrete surrounding it, and form openings in the surrounding earth to enable the flow of natural gas or oil.